clippy_lints/src/methods/unnecessary_to_owned.rs

   1 use super::implicit_clone::is_clone_like;
   2 use super::unnecessary_iter_cloned::{self, is_into_iter};
   3 use clippy_utils::diagnostics::span_lint_and_sugg;
   4 use clippy_utils::source::snippet_opt;
   5 use clippy_utils::ty::{get_associated_type, get_iterator_item_ty, implements_trait, is_copy, peel_mid_ty_refs};
   6 use clippy_utils::visitors::find_all_ret_expressions;
   7 use clippy_utils::{fn_def_id, get_parent_expr, is_diag_item_method, is_diag_trait_item, return_ty};
   8 use clippy_utils::{meets_msrv, msrvs};
   9 use rustc_errors::Applicability;
  10 use rustc_hir::{def_id::DefId, BorrowKind, Expr, ExprKind, ItemKind, Node};
  11 use rustc_infer::infer::TyCtxtInferExt;
  12 use rustc_lint::LateContext;
  13 use rustc_middle::mir::Mutability;
  14 use rustc_middle::ty::adjustment::{Adjust, Adjustment, OverloadedDeref};
  15 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
  16 use rustc_middle::ty::EarlyBinder;
  17 use rustc_middle::ty::{self, ParamTy, PredicateKind, ProjectionPredicate, TraitPredicate, Ty};
  18 use rustc_semver::RustcVersion;
  19 use rustc_span::{sym, Symbol};
  20 use rustc_trait_selection::traits::{query::evaluate_obligation::InferCtxtExt as _, Obligation, ObligationCause};
  21 use rustc_typeck::check::{FnCtxt, Inherited};
  22 use std::cmp::max;
  23
  24 use super::UNNECESSARY_TO_OWNED;
  25
  26 pub fn check<'tcx>(
  27     cx: &LateContext<'tcx>,
  28     expr: &'tcx Expr<'tcx>,
  29     method_name: Symbol,
  30     receiver: &'tcx Expr<'_>,
  31     args: &'tcx [Expr<'_>],
  32     msrv: Option<RustcVersion>,
  33 ) {
  34     if_chain! {
  35         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
  36         if args.is_empty();
  37         then {
  38             if is_cloned_or_copied(cx, method_name, method_def_id) {
  39                 unnecessary_iter_cloned::check(cx, expr, method_name, receiver);
  40             } else if is_to_owned_like(cx, expr, method_name, method_def_id) {
  41                 // At this point, we know the call is of a `to_owned`-like function. The functions
  42                 // `check_addr_of_expr` and `check_call_arg` determine whether the call is unnecessary
  43                 // based on its context, that is, whether it is a referent in an `AddrOf` expression, an
  44                 // argument in a `into_iter` call, or an argument in the call of some other function.
  45                 if check_addr_of_expr(cx, expr, method_name, method_def_id, receiver) {
  46                     return;
  47                 }
  48                 if check_into_iter_call_arg(cx, expr, method_name, receiver, msrv) {
  49                     return;
  50                 }
  51                 check_other_call_arg(cx, expr, method_name, receiver);
  52             }
  53         }
  54     }
  55 }
  56
  57 /// Checks whether `expr` is a referent in an `AddrOf` expression and, if so, determines whether its
  58 /// call of a `to_owned`-like function is unnecessary.
  59 #[allow(clippy::too_many_lines)]
  60 fn check_addr_of_expr(
  61     cx: &LateContext<'_>,
  62     expr: &Expr<'_>,
  63     method_name: Symbol,
  64     method_def_id: DefId,
  65     receiver: &Expr<'_>,
  66 ) -> bool {
  67     if_chain! {
  68         if let Some(parent) = get_parent_expr(cx, expr);
  69         if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) = parent.kind;
  70         let adjustments = cx.typeck_results().expr_adjustments(parent).iter().collect::<Vec<_>>();
  71         if let
  72             // For matching uses of `Cow::from`
  73             [
  74                 Adjustment {
  75                     kind: Adjust::Deref(None),
  76                     target: referent_ty,
  77                 },
  78                 Adjustment {
  79                     kind: Adjust::Borrow(_),
  80                     target: target_ty,
  81                 },
  82             ]
  83             // For matching uses of arrays
  84             | [
  85                 Adjustment {
  86                     kind: Adjust::Deref(None),
  87                     target: referent_ty,
  88                 },
  89                 Adjustment {
  90                     kind: Adjust::Borrow(_),
  91                     ..
  92                 },
  93                 Adjustment {
  94                     kind: Adjust::Pointer(_),
  95                     target: target_ty,
  96                 },
  97             ]
  98             // For matching everything else
  99             | [
 100                 Adjustment {
 101                     kind: Adjust::Deref(None),
 102                     target: referent_ty,
 103                 },
 104                 Adjustment {
 105                     kind: Adjust::Deref(Some(OverloadedDeref { .. })),
 106                     ..
 107                 },
 108                 Adjustment {
 109                     kind: Adjust::Borrow(_),
 110                     target: target_ty,
 111                 },
 112             ] = adjustments[..];
 113         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 114         let (target_ty, n_target_refs) = peel_mid_ty_refs(*target_ty);
 115         let (receiver_ty, n_receiver_refs) = peel_mid_ty_refs(receiver_ty);
 116         // Only flag cases satisfying at least one of the following three conditions:
 117         // * the referent and receiver types are distinct
 118         // * the referent/receiver type is a copyable array
 119         // * the method is `Cow::into_owned`
 120         // This restriction is to ensure there is no overlap between `redundant_clone` and this
 121         // lint. It also avoids the following false positive:
 122         //  https://github.com/rust-lang/rust-clippy/issues/8759
 123         //   Arrays are a bit of a corner case. Non-copyable arrays are handled by
 124         // `redundant_clone`, but copyable arrays are not.
 125         if *referent_ty != receiver_ty
 126             || (matches!(referent_ty.kind(), ty::Array(..)) && is_copy(cx, *referent_ty))
 127             || is_cow_into_owned(cx, method_name, method_def_id);
 128         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 129         then {
 130             if receiver_ty == target_ty && n_target_refs >= n_receiver_refs {
 131                 span_lint_and_sugg(
 132                     cx,
 133                     UNNECESSARY_TO_OWNED,
 134                     parent.span,
 135                     &format!("unnecessary use of `{}`", method_name),
 136                     "use",
 137                     format!(
 138                         "{:&>width$}{}",
 139                         "",
 140                         receiver_snippet,
 141                         width = n_target_refs - n_receiver_refs
 142                     ),
 143                     Applicability::MachineApplicable,
 144                 );
 145                 return true;
 146             }
 147             if_chain! {
 148                 if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
 149                 if implements_trait(cx, receiver_ty, deref_trait_id, &[]);
 150                 if get_associated_type(cx, receiver_ty, deref_trait_id, "Target") == Some(target_ty);
 151                 then {
 152                     if n_receiver_refs > 0 {
 153                         span_lint_and_sugg(
 154                             cx,
 155                             UNNECESSARY_TO_OWNED,
 156                             parent.span,
 157                             &format!("unnecessary use of `{}`", method_name),
 158                             "use",
 159                             receiver_snippet,
 160                             Applicability::MachineApplicable,
 161                         );
 162                     } else {
 163                         span_lint_and_sugg(
 164                             cx,
 165                             UNNECESSARY_TO_OWNED,
 166                             expr.span.with_lo(receiver.span.hi()),
 167                             &format!("unnecessary use of `{}`", method_name),
 168                             "remove this",
 169                             String::new(),
 170                             Applicability::MachineApplicable,
 171                         );
 172                     }
 173                     return true;
 174                 }
 175             }
 176             if_chain! {
 177                 if let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef);
 178                 if implements_trait(cx, receiver_ty, as_ref_trait_id, &[GenericArg::from(target_ty)]);
 179                 then {
 180                     span_lint_and_sugg(
 181                         cx,
 182                         UNNECESSARY_TO_OWNED,
 183                         parent.span,
 184                         &format!("unnecessary use of `{}`", method_name),
 185                         "use",
 186                         format!("{}.as_ref()", receiver_snippet),
 187                         Applicability::MachineApplicable,
 188                     );
 189                     return true;
 190                 }
 191             }
 192         }
 193     }
 194     false
 195 }
 196
 197 /// Checks whether `expr` is an argument in an `into_iter` call and, if so, determines whether its
 198 /// call of a `to_owned`-like function is unnecessary.
 199 fn check_into_iter_call_arg(
 200     cx: &LateContext<'_>,
 201     expr: &Expr<'_>,
 202     method_name: Symbol,
 203     receiver: &Expr<'_>,
 204     msrv: Option<RustcVersion>,
 205 ) -> bool {
 206     if_chain! {
 207         if let Some(parent) = get_parent_expr(cx, expr);
 208         if let Some(callee_def_id) = fn_def_id(cx, parent);
 209         if is_into_iter(cx, callee_def_id);
 210         if let Some(iterator_trait_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
 211         let parent_ty = cx.typeck_results().expr_ty(parent);
 212         if implements_trait(cx, parent_ty, iterator_trait_id, &[]);
 213         if let Some(item_ty) = get_iterator_item_ty(cx, parent_ty);
 214         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 215         then {
 216             if unnecessary_iter_cloned::check_for_loop_iter(cx, parent, method_name, receiver, true) {
 217                 return true;
 218             }
 219             let cloned_or_copied = if is_copy(cx, item_ty) && meets_msrv(msrv, msrvs::ITERATOR_COPIED) {
 220                 "copied"
 221             } else {
 222                 "cloned"
 223             };
 224             // The next suggestion may be incorrect because the removal of the `to_owned`-like
 225             // function could cause the iterator to hold a reference to a resource that is used
 226             // mutably. See https://github.com/rust-lang/rust-clippy/issues/8148.
 227             span_lint_and_sugg(
 228                 cx,
 229                 UNNECESSARY_TO_OWNED,
 230                 parent.span,
 231                 &format!("unnecessary use of `{}`", method_name),
 232                 "use",
 233                 format!("{}.iter().{}()", receiver_snippet, cloned_or_copied),
 234                 Applicability::MaybeIncorrect,
 235             );
 236             return true;
 237         }
 238     }
 239     false
 240 }
 241
 242 /// Checks whether `expr` is an argument in a function call and, if so, determines whether its call
 243 /// of a `to_owned`-like function is unnecessary.
 244 fn check_other_call_arg<'tcx>(
 245     cx: &LateContext<'tcx>,
 246     expr: &'tcx Expr<'tcx>,
 247     method_name: Symbol,
 248     receiver: &'tcx Expr<'tcx>,
 249 ) -> bool {
 250     if_chain! {
 251         if let Some((maybe_call, maybe_arg)) = skip_addr_of_ancestors(cx, expr);
 252         if let Some((callee_def_id, _, recv, call_args)) = get_callee_substs_and_args(cx, maybe_call);
 253         let fn_sig = cx.tcx.fn_sig(callee_def_id).skip_binder();
 254         if let Some(i) = recv.into_iter().chain(call_args).position(|arg| arg.hir_id == maybe_arg.hir_id);
 255         if let Some(input) = fn_sig.inputs().get(i);
 256         let (input, n_refs) = peel_mid_ty_refs(*input);
 257         if let (trait_predicates, _) = get_input_traits_and_projections(cx, callee_def_id, input);
 258         if let Some(sized_def_id) = cx.tcx.lang_items().sized_trait();
 259         if let [trait_predicate] = trait_predicates
 260             .iter()
 261             .filter(|trait_predicate| trait_predicate.def_id() != sized_def_id)
 262             .collect::<Vec<_>>()[..];
 263         if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
 264         if let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef);
 265         if trait_predicate.def_id() == deref_trait_id || trait_predicate.def_id() == as_ref_trait_id;
 266         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 267         if can_change_type(cx, maybe_arg, receiver_ty);
 268         // We can't add an `&` when the trait is `Deref` because `Target = &T` won't match
 269         // `Target = T`.
 270         if n_refs > 0 || is_copy(cx, receiver_ty) || trait_predicate.def_id() != deref_trait_id;
 271         let n_refs = max(n_refs, if is_copy(cx, receiver_ty) { 0 } else { 1 });
 272         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 273         then {
 274             span_lint_and_sugg(
 275                 cx,
 276                 UNNECESSARY_TO_OWNED,
 277                 maybe_arg.span,
 278                 &format!("unnecessary use of `{}`", method_name),
 279                 "use",
 280                 format!("{:&>width$}{}", "", receiver_snippet, width = n_refs),
 281                 Applicability::MachineApplicable,
 282             );
 283             return true;
 284         }
 285     }
 286     false
 287 }
 288
 289 /// Walks an expression's ancestors until it finds a non-`AddrOf` expression. Returns the first such
 290 /// expression found (if any) along with the immediately prior expression.
 291 fn skip_addr_of_ancestors<'tcx>(
 292     cx: &LateContext<'tcx>,
 293     mut expr: &'tcx Expr<'tcx>,
 294 ) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
 295     while let Some(parent) = get_parent_expr(cx, expr) {
 296         if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) = parent.kind {
 297             expr = parent;
 298         } else {
 299             return Some((parent, expr));
 300         }
 301     }
 302     None
 303 }
 304
 305 /// Checks whether an expression is a function or method call and, if so, returns its `DefId`,
 306 /// `Substs`, and arguments.
 307 fn get_callee_substs_and_args<'tcx>(
 308     cx: &LateContext<'tcx>,
 309     expr: &'tcx Expr<'tcx>,
 310 ) -> Option<(DefId, SubstsRef<'tcx>, Option<&'tcx Expr<'tcx>>, &'tcx [Expr<'tcx>])> {
 311     if_chain! {
 312         if let ExprKind::Call(callee, args) = expr.kind;
 313         let callee_ty = cx.typeck_results().expr_ty(callee);
 314         if let ty::FnDef(callee_def_id, _) = callee_ty.kind();
 315         then {
 316             let substs = cx.typeck_results().node_substs(callee.hir_id);
 317             return Some((*callee_def_id, substs, None, args));
 318         }
 319     }
 320     if_chain! {
 321         if let ExprKind::MethodCall(_, recv, args, _) = expr.kind;
 322         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
 323         then {
 324             let substs = cx.typeck_results().node_substs(expr.hir_id);
 325             return Some((method_def_id, substs, Some(recv), args));
 326         }
 327     }
 328     None
 329 }
 330
 331 /// Returns the `TraitPredicate`s and `ProjectionPredicate`s for a function's input type.
 332 fn get_input_traits_and_projections<'tcx>(
 333     cx: &LateContext<'tcx>,
 334     callee_def_id: DefId,
 335     input: Ty<'tcx>,
 336 ) -> (Vec<TraitPredicate<'tcx>>, Vec<ProjectionPredicate<'tcx>>) {
 337     let mut trait_predicates = Vec::new();
 338     let mut projection_predicates = Vec::new();
 339     for predicate in cx.tcx.param_env(callee_def_id).caller_bounds() {
 340         match predicate.kind().skip_binder() {
 341             PredicateKind::Trait(trait_predicate) => {
 342                 if trait_predicate.trait_ref.self_ty() == input {
 343                     trait_predicates.push(trait_predicate);
 344                 }
 345             },
 346             PredicateKind::Projection(projection_predicate) => {
 347                 if projection_predicate.projection_ty.self_ty() == input {
 348                     projection_predicates.push(projection_predicate);
 349                 }
 350             },
 351             _ => {},
 352         }
 353     }
 354     (trait_predicates, projection_predicates)
 355 }
 356
 357 fn can_change_type<'a>(cx: &LateContext<'a>, mut expr: &'a Expr<'a>, mut ty: Ty<'a>) -> bool {
 358     for (_, node) in cx.tcx.hir().parent_iter(expr.hir_id) {
 359         match node {
 360             Node::Stmt(_) => return true,
 361             Node::Block(..) => continue,
 362             Node::Item(item) => {
 363                 if let ItemKind::Fn(_, _, body_id) = &item.kind
 364                 && let output_ty = return_ty(cx, item.hir_id())
 365                 && let local_def_id = cx.tcx.hir().local_def_id(item.hir_id())
 366                 && Inherited::build(cx.tcx, local_def_id).enter(|inherited| {
 367                     let fn_ctxt = FnCtxt::new(&inherited, cx.param_env, item.hir_id());
 368                     fn_ctxt.can_coerce(ty, output_ty)
 369                 }) {
 370                     if has_lifetime(output_ty) && has_lifetime(ty) {
 371                         return false;
 372                     }
 373                     let body = cx.tcx.hir().body(*body_id);
 374                     let body_expr = &body.value;
 375                     let mut count = 0;
 376                     return find_all_ret_expressions(cx, body_expr, |_| { count += 1; count <= 1 });
 377                 }
 378             }
 379             Node::Expr(parent_expr) => {
 380                 if let Some((callee_def_id, call_substs, recv, call_args)) = get_callee_substs_and_args(cx, parent_expr)
 381                 {
 382                     let fn_sig = cx.tcx.fn_sig(callee_def_id).skip_binder();
 383                     if let Some(arg_index) = recv.into_iter().chain(call_args).position(|arg| arg.hir_id == expr.hir_id)
 384                         && let Some(param_ty) = fn_sig.inputs().get(arg_index)
 385                         && let ty::Param(ParamTy { index: param_index , ..}) = param_ty.kind()
 386                     {
 387                         if fn_sig
 388                             .inputs()
 389                             .iter()
 390                             .enumerate()
 391                             .filter(|(i, _)| *i != arg_index)
 392                             .any(|(_, ty)| ty.contains(*param_ty))
 393                         {
 394                             return false;
 395                         }
 396
 397                         let mut trait_predicates = cx.tcx.param_env(callee_def_id)
 398                             .caller_bounds().iter().filter(|predicate| {
 399                             if let PredicateKind::Trait(trait_predicate) =  predicate.kind().skip_binder()
 400                                 && trait_predicate.trait_ref.self_ty() == *param_ty {
 401                                     true
 402                                 } else {
 403                                 false
 404                             }
 405                         });
 406
 407                         let new_subst = cx.tcx.mk_substs(
 408                             call_substs.iter()
 409                                 .enumerate()
 410                                 .map(|(i, t)|
 411                                      if i == (*param_index as usize) {
 412                                          GenericArg::from(ty)
 413                                      } else {
 414                                          t
 415                                      }));
 416
 417                         if trait_predicates.any(|predicate| {
 418                             let predicate = EarlyBinder(predicate).subst(cx.tcx, new_subst);
 419                             let obligation = Obligation::new(ObligationCause::dummy(), cx.param_env, predicate);
 420                             !cx.tcx
 421                                 .infer_ctxt()
 422                                 .enter(|infcx| infcx.predicate_must_hold_modulo_regions(&obligation))
 423                         }) {
 424                             return false;
 425                         }
 426
 427                         let output_ty = fn_sig.output();
 428                         if output_ty.contains(*param_ty) {
 429                             if let Ok(new_ty)  = cx.tcx.try_subst_and_normalize_erasing_regions(
 430                                 new_subst, cx.param_env, output_ty) {
 431                                 expr = parent_expr;
 432                                 ty = new_ty;
 433                                 continue;
 434                             }
 435                             return false;
 436                         }
 437
 438                         return true;
 439                     }
 440                 } else if let ExprKind::Block(..) = parent_expr.kind {
 441                     continue;
 442                 }
 443                 return false;
 444             },
 445             _ => return false,
 446         }
 447     }
 448
 449     false
 450 }
 451
 452 fn has_lifetime(ty: Ty<'_>) -> bool {
 453     ty.walk().any(|t| matches!(t.unpack(), GenericArgKind::Lifetime(_)))
 454 }
 455
 456 /// Returns true if the named method is `Iterator::cloned` or `Iterator::copied`.
 457 fn is_cloned_or_copied(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 458     (method_name.as_str() == "cloned" || method_name.as_str() == "copied")
 459         && is_diag_trait_item(cx, method_def_id, sym::Iterator)
 460 }
 461
 462 /// Returns true if the named method can be used to convert the receiver to its "owned"
 463 /// representation.
 464 fn is_to_owned_like<'a>(cx: &LateContext<'a>, call_expr: &Expr<'a>, method_name: Symbol, method_def_id: DefId) -> bool {
 465     is_clone_like(cx, method_name.as_str(), method_def_id)
 466         || is_cow_into_owned(cx, method_name, method_def_id)
 467         || is_to_string_on_string_like(cx, call_expr, method_name, method_def_id)
 468 }
 469
 470 /// Returns true if the named method is `Cow::into_owned`.
 471 fn is_cow_into_owned(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 472     method_name.as_str() == "into_owned" && is_diag_item_method(cx, method_def_id, sym::Cow)
 473 }
 474
 475 /// Returns true if the named method is `ToString::to_string` and it's called on a type that
 476 /// is string-like i.e. implements `AsRef<str>` or `Deref<str>`.
 477 fn is_to_string_on_string_like<'a>(
 478     cx: &LateContext<'_>,
 479     call_expr: &'a Expr<'a>,
 480     method_name: Symbol,
 481     method_def_id: DefId,
 482 ) -> bool {
 483     if method_name != sym::to_string || !is_diag_trait_item(cx, method_def_id, sym::ToString) {
 484         return false;
 485     }
 486
 487     if let Some(substs) = cx.typeck_results().node_substs_opt(call_expr.hir_id)
 488         && let [generic_arg] = substs.as_slice()
 489         && let GenericArgKind::Type(ty) = generic_arg.unpack()
 490         && let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref)
 491         && let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef)
 492         && (implements_trait(cx, ty, deref_trait_id, &[cx.tcx.types.str_.into()]) ||
 493             implements_trait(cx, ty, as_ref_trait_id, &[cx.tcx.types.str_.into()])) {
 494             true
 495         } else {
 496             false
 497         }
 498 }